Well, yes and no. Officially we run society along a bunch of rules which, I guess, are black and white in the way a flock of penguins in a snowstorm at night is black and white. Unofficially there is a lot of psychology going on in how we run things (kind of inevitably), but it is not mindfully applied psychology, more's the pity. You're putting your finger right on the problem there. It is fairly easy to understand what makes some people listen to hate preachers (I could explain, but that would be another wall-of-text), but if we do we have to confront some pertinent flaws in how we raise our children and what kind of society we raise them in. We'd also have to confront why so many people in the Middle East have taken a dislike to us over the last 60 years or so. And we'd have to examine the psychology of religion and the religious rarely feel very comfortable with that. We'd be staring into some big abysses and find them staring right back at us. Most people prefer to live in denial. That's one way to define an extremist. Another would be to define them in terms of the nature of their beliefs and actions rather than their prevalence. But I'm saying that those who fail to distance themselves from extremists claiming to act in their name will get lumped with them. That doesn't mean that they belong there, but that is how people categorise things. Every action is born from thought. We can certainly game the system. If you understand what a person thinks, feels and does, you can make an informed guess of what he is likely to think, feel and do next in response to something. We can thus influence the likelihood of a certain behaviour. But we cannot control it and we cannot make it happen. Well, there was a lot of gaming the system involved there. Post WWII the Marshall Plan comes to mind, as does the instatement, support and subsequent overthrow of Saddam Hussein and the formation of an interim government for Iraq. Historically speaking no, we haven't, but that's another debate.